Method and apparatus for retrieving data from a broadcast signal

ABSTRACT

A broadcast signal is received that includes a data identifier that identifies data associated with the broadcast signal. The broadcast signal also includes the data associated with the broadcast signal encoded in the broadcast signal. The data associated with the broadcast signal includes an indicator to ignore the data identifier contained in the broadcast signal. The system decodes the data encoded in the broadcast signal while ignoring the data identifier contained in the broadcast signal. The indicator to ignore the data identifier contained in the broadcast signal may include an associated time period during which the data identifier should be ignored. The data identifier is broadcast in scan line twenty-one of a broadcast image. The data associated with the broadcast signal is encoded in vertical blanking interval lines of a broadcast image.

This application is a continuation-in-part of application Ser. No.09/412,839, filed Oct. 5, 1999, entitled “Trigger Having A TimeAttribute”, now U.S. Pat. No. 6,415,438, and is a continuation-in-partof application Ser. No. 09/345,247, filed Jun. 30, 1999, entitled“Interactive Television Triggers Having Connected Content/DisconnectedContent Attribute”, now U.S. Pat. No. 6,668,378.

TECHNICAL FIELD

This invention relates to a system that retrieves data from a broadcastsignal, such as a television broadcast signal.

BACKGROUND

Broadcast television in the United States is broadcast in accordancewith the National Television Standards Committee (NTSC) broadcasttelevision format standard. The NTSC broadcast format provides for thetransmission of approximately thirty image frames per second. Aparticular frame includes two interlaced fields, in which each fieldincludes 265½ horizontal scan lines. FIG. 1 illustrates an exampletelevision broadcast frame 10 in accordance with the NTSC standard.Broadcast frame 10 may also be referred to as a “broadcast image.”

The broadcast and display of frame 10 is described in connection with aconventional analog television having a cathode ray tube (CRT) with anelectron beam. A receiver portion of the television receives thebroadcast NTSC signal and controls the electron beam such that theelectron beam is scanned across the screen of the CRT to generate theappropriate image. The first nine horizontal scan lines (lines 1-9) ofthe frame 10 are used to synchronize the television receiver and toreturn the electron beam to the top of the screen. The electron beam isdisabled (also referred to as “blanked”) during the scan time of thefirst twenty-one scan lines so that the electron beam does not generatea visible line from the bottom of the screen to the top of the screenwhen being returned to the top of the screen. The first twenty-one scanlines are commonly referred to as the “vertical blanking interval” lines(or VBI lines).

The odd scan lines of the frame (i.e., frame line 1, frame line 3, etc.)are received first and are referred to as the “odd field”. The firsttwenty-one of these odd lines are the VBI lines. These first twenty-onelines synchronize the television receiver for the subsequent scanning ofthe horizontal scan lines of a viewable portion 12 of the frame 10.During each horizontal scan line, the electron beam scans from left toright across the screen. When the electron beam reaches the right edgeof the screen, the electron beam is returned to the left edge of thescreen in preparation for the scanning of the next scan line. After thescanning of each odd scan line in viewable portion 12, the electron beamis “blanked” as the electron beam is returned to left edge of the screenin preparation for the start of the next scan line. This blanking timeis referred to as the “horizontal blanking interval” of the frame, whichis indicated by a region 14 in FIG. 1.

After the last odd scan line has finished, the even scan lines of theframe (i.e., frame line 2, frame line 4, etc.) are received and arereferred to as the “even field”. As with the odd field discussed above,the first twenty-one scan lines of the even field are VBI lines. Theelectron beam is blanked during the scanning of the even VBI lines suchthat the electron beam can be returned to the top of the screen withoutgenerating a line on the screen. After the scanning of all the even VBIlines, the even scan lines of viewable portion 12 are scanned in amanner similar to the scanning of the odd scan lines discussed above.The viewable horizontal scan lines of the odd and even fields togethercause the electron beam to scan across the screen of the television tocreate the viewable television image.

Generally, the entire vertical blanking interval is not required forvertical synchronization and returning the electron beam to the top ofthe screen. Typically, only VBI lines 1-9 of each field (i.e., the oddfield and the even field) are used for these purposes. Thus, theremaining twelve VBI lines (lines 10-21) are available for communicatingother information.

For example, VBI line 21 provides a low speed communication sub-channel(the “line 21 sub-channel”). Data is encoded in the line 21 sub-channelin accordance with the encoding technique set forth in EIA-608, which isreserved by the Federal Communication Commission (FCC) for captioningservices. The line sub-channel can transmit textual information, thecurrent time, “V-chip” program rating codes, and closed captioninginformation. For example, a television receiver captures the closedcaptioning information and displays it as a text subtitle along with thetelevision video to assist the hearing impaired.

VBI lines 10-20 are available for a higher-speed communicationsub-channel for the communication of data. Data can be encoded in VBIlines 10-20 at a data rate sufficient to communicate web page contentalong with the television content being transmitted. The web pagecontent is received and stored locally in the television receiver forfuture access. Later, when the web page content is to be displayed at aparticular time in the television video, a “trigger” that identifies theweb page content (e.g., by file name) is broadcast to the televisionreceiver. When the trigger is received, the associated web page contentis retrieved from the local storage device and displayed on thetelevision screen.

However, certain televisions do not support the transmission of dataover the VBI lines as discussed above. Furthermore, certain broadcastsystems (such as digitally compressed satellite feeds and digital cablesystems) may prevent the VBI-based information from being delivered tocapable receivers. Thus, an alternate system sends information andtriggers using line 21 instead of the VBI lines. Typically, theinformation transmitted using line 21 is relatively short, such as auniform resource locator (URL) identifying the location of web pagecontent to be retrieved by a television receiver (e.g., via a telephoneline or other network connection). Since the television broadcastertransmits the same signal to many televisions, the broadcaster cannottailor its signal to match the capabilities of a particular televisionreceiver.

The system described herein addresses these and other problems byproviding a television broadcast method and system that supports thetransmission of data to various types of television receivers.

SUMMARY

The method and apparatus for retrieving data from a broadcast signaldescribed herein allows a single television broadcast signal to supportmultiple types of television receivers. Different methods are used tocommunicate data and data identifiers along with the television programcontent, thereby allowing different types of television receivers toretrieve data from the broadcast signal.

In one implementation, a broadcast signal is received that includes adata identifier that identifies data associated with the broadcastsignal. The broadcast signal also includes the data associated with thebroadcast signal encoded in the broadcast signal. The data associatedwith the broadcast signal includes an indicator to ignore the dataidentifier contained in the broadcast signal. The procedure decodes thedata encoded in the broadcast signal and ignores the data identifiercontained in the broadcast signal.

In another embodiment, the indicator to ignore the data identifiercontained in the broadcast signal includes a time period during whichthe data identifier should be ignored.

In a particular embodiment, the broadcast signal includes a broadcastimage and the data identifier is broadcast in line twenty-one of thebroadcast image.

In particular embodiments, the data associated with the broadcast signalis encoded in vertical blanking interval lines of the broadcast image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example television broadcast frame in accordancewith the NTSC standard.

FIG. 2 illustrates an exemplary network environment in which atelevision receiving system receives and transmits data across theInternet and receives television signals from a television broadcastsource.

FIG. 3 illustrates an embodiment of a television receiving system.

FIG. 4 is a block diagram of a receiver capable of receiving televisionsignals and network data, and generating video signals for display on atelevision.

FIG. 5 is a flow diagram illustrating a procedure for generating abroadcast television signal that includes data and data identifiers.

FIG. 6 is a flow diagram illustrating a procedure for decodinginformation contained in a broadcast television signal.

DETAILED DESCRIPTION

The method and apparatus for retrieving data from a broadcast signaldescribed herein provides support for multiple types of televisionreceivers using a single television broadcast signal. Alternatemechanisms are provided to communicate data and data identifiers alongwith the television program content. Using a first mechanism, a dataidentifier is transmitted in scan line twenty-one. This data identifieridentifies the location of data associated with the television program.Another mechanism reads the data associated with the television programfrom the vertical blanking interval lines.

Various examples and embodiments are described herein with reference totelevision broadcast signals. However, the systems and proceduresdescribed herein can be used with any type of broadcast signal, and arenot limited to television signals. Furthermore, examples containedherein describe the systems and procedures with respect to a televisionsystem. However, the teachings of the present invention can be appliedto any type of display device, such as direct view televisions,projection television systems, and flat panel displays.

FIG. 2 illustrates an exemplary network environment 100 in which atelevision receiving system 108 transmits and receives data across theInternet 110 and receives television signals from a television broadcastsource 112. A client 102, servers 104 and 106, and the televisionreceiving system 108 are coupled to one another through the Internet110. Television receiving system 108 is capable of receiving varioustypes of data from one or more devices coupled to the Internet 110.Television receiving system 108 is also coupled to the televisionbroadcast source 112, which broadcasts television signals via acommunication link 114. Television receiving system 108 may receivetelevision signals from source 112 via cable, satellite, microwave,computer network, terrestrial (over the air) broadcast, or any othercommunication medium. Although not shown in FIG. 2, television broadcastsource 112 may have an associated server or other device coupled to theInternet 110, which allows the source 112 to broadcast televisionsignals via one medium (e.g., cable) and transmit other data related tothe television broadcast via the Internet 110. Alternatively, televisionbroadcast source 112 may transmit television signals as well as otherdata related to the television signals via the Internet 110.

FIG. 3 illustrates an embodiment of the television receiving system 108.A receiver 200, such as a set-top box, receives a broadcast televisionsignal 206 from a television broadcast source (such as source 112 inFIG. 2). The receiver 200 communicates data bi-directionally on a datacommunication link 212. Data communication link 212 may use any type ofcommunication medium and any communication protocol. In a particularembodiment, data communication link 212 is a telephone line thatprovides a data connection to the Internet or another data communicationnetwork. Receiver 200 is coupled to a video storage device 204, whichstores television signals and other data. Receiver 200 is also coupledto a television 202 via a video communication link 208. Videocommunication link 208 may be a radio frequency (RF), s-video, compositevideo, component video, or other video link. Television 202 may be anytype of display device or projection device using any type of display orprojection technology, including projection display systems and flatpanel displays.

Receiver 200 receives broadcast television signal 206 and displays thereceived signal on television 202 and/or stores the received signal onvideo storage device 204. Alternatively, receiver 200 may receivetelevision signals via data communication link 212. Furthermore,additional information associated with the received television signalmay be received and/or transmitted on data communication link 212. Forexample, web page content associated with a particular televisionbroadcast may be sent via communication link 212 or encoded into thebroadcast itself. Although receiver 200, television 202, and videostorage device 204 are shown in FIG. 3 as separate devices, any two ormore of these devices may be combined into a single device.

FIG. 4 is a block diagram of the receiver 200 shown in FIG. 3. Asdiscussed above, receiver 200 is capable of receiving television signalsand network data and generating video signals for display on atelevision. Additionally, the receiver 200 can be used, for example, toperform various procedures necessary to record and play back televisionprograms and allow a viewer to interact with the source of a televisionbroadcast (e.g., via a data communication network). Receiver 200includes a television interface 224, such as a television tuner, whichreceives the broadcast television signal 206 from a television broadcastsource. A data interface 226 transmits and receives data acrosscommunication link 212, which is typically coupled to a datacommunication network such as the Internet. Data interface 226 typicallyincludes a modem or other bi-directional data communication device.Receiver 200 also includes a video storage device interface 228, whichcommunicates with one or more video storage devices, such as device 204shown in FIG. 3, via communication link 210.

Receiver 200 includes one or more processors 230, a random access memory(RAM) 232, a read-only memory (ROM) 234, and a mass storage device 236.Processor 230 is capable of implementing the various procedures andoperations discussed herein. RAM 232 and mass storage device 236 providefor the storage of data, instructions, and other information used byprocessor 230 during the operation of receiver 200. ROM 234 storesvarious parameters and basic operating instructions used, for example,by processor 230.

An audio interface 238 communicates audio data across an audiocommunication link 220. Similarly, a video interface 240 communicatesvideo data across a video communication link 222. In a particularembodiment, audio interface 238 and video interface 240 are combinedinto a single audio/video interface which communicates audio and videoinformation across an audio/video communication link. Although not shownin FIG. 4, receiver 200 may also include a remote control interface thatallows a television viewer to control the functions of the receiverusing a handheld remote control device.

Generally, the processor 230 of receiver 200 is programmed by means ofinstructions stored at different times in various computer-readablestorage media of the receiver, such as RAM 232 and mass storage 236. Thesystem described herein includes various types of computer-readablestorage media when such media contains instructions or programs forimplementing the steps described herein in conjunction with a processor.The system also includes the receiver itself when programmed accordingto the methods and techniques described herein. Alternatively, thesesystems can be implemented in hardware or a combination of hardware,software, and/or firmware. For example, one or more application specificintegrated circuits (ASICs) could be programmed to carry out the systemsand procedures discussed herein.

As used herein, a television program is typically defined as aparticular television show or event (such as a sporting event or aconcert). However, a television program may refer to a portion of anevent (e.g., the first hour of a concert or the first part of amulti-part program). A television program may have a known length (suchas a movie or a weekly episode of a pre-recorded program) or unknownlength, such as a sporting event.

As discussed above, different methods are used to encode data into atelevision broadcast signal. A first method uses line twenty-one of thetelevision signal to broadcast data, such as a URL or other dataidentifier, which is related to the current television program or anupcoming television program. The URL or other data identifier broadcastwith the television signal is commonly referred to as a “trigger”. Afterreceiving the URL, the television receiver (e.g., a set top box)contacts the web site associated with the URL and retrieves the web pagecontent from the web site. Typically, the URL (or other identifier) isbroadcast at periodic intervals using line twenty-one.

Another method of encoding data into a television broadcast signal usesthe VBI lines to transmit data associated with the television programcurrently being broadcast or scheduled to be broadcast in the future.The data transmitted using the VBI lines may include, for example, webpage content from a web server. In one embodiment, the data includes asession description protocol (SDP) announcement that identifies thecontent and attributes of the data that follows. SDP is intended fordescribing multimedia sessions for the purposes of session announcement,session invitation, and other forms of multimedia session initiation. Amultimedia session is a set of multimedia senders and receivers and thedata streams flowing from senders to receivers. A multimedia conference(two or more communicating users) is an example of a multimedia session.A session announcement is a mechanism by which a session description isconveyed to users in a proactive fashion, i.e., the session descriptionwas not explicitly requested by the user. A session description is aformat for conveying sufficient information to discover and participatein a multimedia session.

SDP includes a session name and purpose, time(s) the session is active,the media comprising the session, information to receive those media(addresses, ports, formats, etc.), information regarding the bandwidthto be used by the conference, and contact information for the personresponsible for the session. Generally, SDP conveys sufficientinformation to allow a user to join a session and to announce theresources to be used. For example, SDP may include the type of media(video, audio, etc.), the transport protocol, and the format of thevideo (such as MPEG video). If working with a multicast stream, SDP alsoconveys the multicast address for the media and the transport port forthe media. If working with a unicast session, SDP conveys the remoteaddress for the media, and the transport port for the contact address.Additional information regarding SDP is available from the MultipartyMultimedia Session Control (MMUSIC) working group of the InternetEngineering Task Force (specifically, a document identified as “Requestfor Comments: 2327” dated April 1998, and any future versions thereof).

Older television receivers or set top boxes may only support the firstmethod, receiving data (e.g., triggers) from line twenty-one, but do notsupport the identification of data contained in the VBI lines. Sincethese older devices cannot identify data contained in the VBI lines,they use the triggers broadcast in line twenty-one to identify thesource of data to be downloaded, for example, from a web server. Newertelevision receivers or set top boxes may support both the first method(i.e., line twenty-one triggers) and the second method (i.e.,transmitting data in the VBI lines).

To provide support for both older television receivers and newertelevision receivers, television broadcasters may use both methodsdiscussed above to communicate data along with a television signal. Forexample, line twenty-one contains a URL to a particular web site, suchas: www.acme.com, which causes the television receiver to retrieve theweb page content from the web site. Additionally, the web page contentis broadcast in the VBI lines for the benefit of those televisionreceivers capable of retrieving data from the VBI lines. In thisexample, the data transmitted in the VBI lines is the same as the datapointed to by the URL. Therefore, it is not necessary for a televisionreceiver to read the data from the VBI lines and respond to the linetwenty-one trigger, because the two sets of data are identical. In thissituation, it is necessary to instruct television receivers capable ofreading the data in the VBI lines to ignore the triggers received inline twenty-one, thereby avoiding the retrieval of redundant data.

To instruct television receivers to ignore the line twenty-one triggers,a new attribute is used in the SDP announcement that identifies the URLor other data identifiers that should be ignored. Additionally, theattribute identifies the time period during which the televisionreceiver should ignore the particular line twenty-one triggers. Thefollowing is an example SDP announcement that instructs televisionreceivers to ignore line twenty-one triggers associated with thewww.acme.com web site.

a=tve-ignore: www.acme.com/* [t=30]

In this SDP announcement, “a” indicates an arbitrary attribute and“tve-ignore” indicates that the attribute is instructing the televisionreceiver to ignore certain line twenty-one triggers. The final portionof the SDP announcement indicates the line twenty-one triggers toignore. The “*” character is a wildcard character. In this example, anyline twenty-one trigger identifying a URL beginning with “www.acme.com”will be ignored by the television receiver for the time period stated(e.g., for the next thirty minutes).

In another example, the SDP announcement is as follows:

a=tve-ignore: *www.hdd.com/* [t=12:00,13:00]

In this SDP announcement, any line twenty-one trigger identifying a URLcontaining “www.hdd.com” will be ignored by the television receiver forthe time period stated (e.g., between noon and 1:00 p.m.). The two “*”characters cause the television receiver to ignore all line twenty-onetriggers that contain “www.hdd.com” anywhere in the trigger.

Since the SDP announcement is sent in the VBI lines, it does not affectthe operation of older television receivers that cannot read data fromthe VBI lines. Thus, the older television receivers will not ignore theline twenty-one triggers because the SDP announcement is not understoodby the older receivers.

FIG. 5 is a flow diagram illustrating a procedure for generating abroadcast television signal that includes data and data identifiers. Atelevision broadcast source generates a television broadcast that hasseparate associated data (block 270). For example, one or more web pagesmay be associated with a particular television broadcast. These webpages provide, for example, additional information about the televisionprogram and/or provide an opportunity for a viewer to activate aninteractive television mode. The television broadcast source includesencoded line twenty-one triggers in the television broadcast signal(block 272). The line twenty-one triggers identify the data associatedwith the television broadcast. The television broadcast source alsoincludes encoded data associated with the television broadcast in theVBI lines of the television broadcast signal (block 274). Additionally,the television broadcast source includes an SDP announcement of the typediscussed above to indicate that the line twenty-one triggers in thetelevision broadcast signal should be ignored (block 276). Since thetelevision broadcast signal contains both the line twenty-one triggersand the data in the VBI lines, this single television broadcast signalsupports both older television receivers and newer television receivers.

FIG. 6 is a flow diagram illustrating a procedure for decodinginformation contained in a broadcast television signal. In this example,the broadcast television signal contains both line twenty-one triggersidentifying a set of data and the data itself, which is transmitted inthe VBI lines. A television receiver receives the broadcast televisionsignal including the line twenty-one triggers and the data contained inthe VBI lines (block 280). The procedure then determines whether thetelevision receiver is able to decode data in the VBI lines (block 282).If not, the procedure branches to block 284 where the televisionreceiver decodes the data identifiers contained in the line twenty-onetriggers. The television receiver then retrieves the data using the dataidentifier (block 286).

If the television receiver is capable of decoding data in the VBI lines,then the television receiver decodes that data, which may include one ormore SDP announcements indicating that particular line twenty-onetriggers in the television broadcast signal should be ignored (block288). As discussed above, the SDP announcement may include a particulartime during which the line twenty-one triggers should be ignored. Block290 determines whether any received SDP announcements indicate a linetwenty-one trigger to ignore. If not, the procedure branches to block284, where the television receiver decodes the data identifierscontained in the line twenty-on triggers. If an SDP announcementindicates a line twenty-one trigger to ignore, then the televisionreceiver decodes the data contained in the VBI lines and ignores theline twenty-one triggers identified in the SDP announcement (block 292).

Thus, a system has been described that allows a single televisionbroadcast signal to support multiple types of television receivers byproviding alternate mechanisms to communicate data and data identifiersalong with the television program content. Further, television receiverscapable of reading data from both the VBI lines and from line twenty-onetriggers are instructed to ignore line twenty-one triggers that containredundant data.

Although the description above uses language that is specific tostructural s features and/or methodological acts, it is to be understoodthat the invention defined in the appended claims is not limited to thespecific features or acts described. Rather, the specific features andacts are disclosed as exemplary forms of implementing the invention.

What is claimed is:
 1. A method comprising: receiving a broadcast signalincluding a data identifier that identifies data associated with thebroadcast signal, wherein the broadcast signal further includes the dataassociated with the broadcast signal encoded in the broadcast signal,and wherein the data associated with the broadcast signal includes anindicator to ignore the data identifier contained in the broadcastsignal; decoding the data encoded in the broadcast signal; and ignoringthe data identifier contained in the broadcast signal.
 2. A method asrecited in claim 1 wherein ignoring the data identifier contained in thebroadcast signal includes ignoring the data identifier if the dataidentifier matches another data identifier associated with theindicator.
 3. A method as recited in claim 1 wherein the indicator toignore the data identifier contained in the broadcast signal includes atime period during which the data identifier should be ignored.
 4. Amethod as recited in claim 1 wherein the broadcast signal includes abroadcast image, and wherein the data identifier is broadcast in linetwenty-one of the broadcast image.
 5. A method as recited in claim 1wherein the data identifier identifies a data source which stores thesame data that is encoded in the broadcast signal.
 6. A method asrecited in claim 1 wherein the broadcast signal includes a broadcastimage, and wherein the data associated with the broadcast signal isencoded in vertical blanking interval lines of the broadcast image.
 7. Amethod comprising: receiving a television broadcast signal including adata identifier that identifies data associated with the broadcastsignal, the data identifier being broadcast in line twenty-one of abroadcast image, the broadcast signal further including the dataassociated with the broadcast signal encoded in vertical blankinginterval lines of the broadcast image, and wherein the data associatedwith the broadcast signal includes an indicator to ignore the dataidentifier contained in the broadcast signal; decoding the data encodedin the broadcast signal; and ignoring the data identifier contained inthe broadcast signal.
 8. A method as recited in claim 7 wherein theindicator to ignore the data identifier contained in the broadcastsignal includes an associated time period during which the dataidentifier should be ignored.
 9. A method as recited in claim 7 whereinthe data identifier identifies a data source which stores the same datathat is encoded in the broadcast signal.
 10. One or morecomputer-readable memories containing a computer program that isexecutable by a processor to perform the method recited in claim
 7. 11.A method comprising: identifying data associated with a televisionbroadcast; generating a television broadcast signal including a dataidentifier that identifies the data associated with the televisionbroadcast and including the data associated with the television program,wherein the data associated with the broadcast signal includes anindicator to ignore the data identifier contained in the broadcastsignal; and transmitting the television broadcast signal to a pluralityof television receivers.
 12. A method as recited in claim 11 wherein thedata identifier is contained in line twenty-one of a broadcast image.13. A method as recited in claim 11 wherein the data identifieridentifies a data source which stores the same data that is included inthe broadcast signal.
 14. A method as recited in claim 11 wherein thedata that is included in the broadcast signal is contained in verticalblanking interval lines of a broadcast image.
 15. One or morecomputer-readable memories containing a computer program that isexecutable by a processor to perform the method recited in claim
 11. 16.An apparatus comprising a television receiver configured to receive atelevision broadcast signal including a data identifier that identifiesdata associated with the broadcast signal, the broadcast signal furtherincluding the data associated with the broadcast signal encoded in thebroadcast signal, wherein the data associated with the broadcast signalincludes an indicator to ignore the data identifier contained in thebroadcast signal, the television receiver further to decode the dataencoded in the broadcast signal and to ignore the data identifiercontained in the broadcast signal.
 17. An apparatus as recited in claim16 wherein the television receiver decodes data associated with thebroadcast signal from vertical blanking interval lines of a broadcastimage.
 18. An apparatus as recited in claim 16 wherein the indicator toignore the data identifier contained in the broadcast signal includes anassociated time period during which the data identifier should beignored.
 19. An apparatus as recited in claim 16 wherein the apparatusis a set top box.
 20. One or more computer-readable media having storedthereon a computer program that, when executed by one or moreprocessors, causes the one or more processors to: receive a broadcastsignal including a data identifier that identifies data associated withthe broadcast signal, the broadcast signal further including the dataassociated with the broadcast signal encoded in the broadcast signal,and wherein the data associated with the broadcast signal includes anindicator to ignore the data identifier contained in the broadcastsignal; decode the data encoded in the broadcast signal; and ignore thedata identifier contained in the broadcast signal.
 21. One or morecomputer-readable media as recited in claim 20 wherein the dataidentifier is broadcast in scan line twenty-one of a broadcast image.22. One or more computer-readable media as recited in claim 20 whereinthe data associated with the broadcast signal is encoded in verticalblanking interval lines of a broadcast image.